Climate effects on planktonic food quality and trophic transfer in Arctic Marginal Ice Zones II

-A warmer climate with less extensive ice cover will potentially lead to higher total primary production, which may increase the overall secondary production in the Arctic. However, altered climate conditions will affect timing, quantity and quality of ice algal and phytoplankton food sources with extensive implications for grazers. Among Arctic zooplankton, the relatively large endemic copepod Calanus glacialis (3-5 mm) comprises up to 80% of the zooplankton biomass in seasonal ice covered shelf seas. Due to its ability to convert low-energy carbohydrates and proteins in algae into high-energy wax ester lipids, it is extremely lipid-rich (50-70% lipids of its dry weight) and thus a very important food item for higher trophic levels, such as fish, birds and mammals. This fatty copepod ensures that the essential omega-3 and omega-6 fatty acids, produced exclusively by marine algae, are efficiently channeled to higher trophic levels. The fate of this nutritious copepod in a warmer Arctic is thus of vital importance to predict the vulnerability of Arctic marine ecosystems to climate change. In the project Climate effects on planktonic food quality and trophic transfer in Arctic Marginal ice zones II (CLEOPATRA II, NRC 2012-2015) we combined extensive year-round field surveys with controlled laboratory experiments, and optimal life history modelling to ultimately arrive to C. glacialis resilience to climate change. Calanus glacialis uses 1 to 2 years to complete its life cycle. In the laboratory, we found that C. glacialis is capable of producing viable eggs on internal reserves only (capital breeding), but that egg production rates was 10 times higher for fed females. Field studies confirmed that high egg production rates first occur when food is plentiful. Despite actively feeding, females almost depleted their internal lipid resources, suggesting that C. glacialis has evolved a mixed strategy, a strategy allowing spawning over several months, ensuring that some eggs will always make it. Interestingly, the amount of lipids invested per egg varied with food availability, suggesting a reproduction strategy not previously described for Calanus glacialis: when food is absent or low, females invest in fewer but more lipid-rich eggs; when food is favourable females produce many, but in lipid-poor eggs. Calanus glacialis is a seasonal migrator. The time frame for seasonal descent to deeper water was rather narrow (July-August), while the seasonal ascent was much earlier than previously assumed and spanned over 4 months from November to March. Replacing heavier ions with lighter ones and vice versa showed to be the most likely buoyancy regulation, and not lipids. From our individual image-analyses we found that the largest and most lipid-rich individuals migrated down first, and these individuals were also the first to molt to adults, and most likely to males, since males were larger and appeared before females. Interestingly, the internal pH (haemolymph) in the copepods revealed a strong seasonal pattern with extremely low (5.5) pH in winter and high (7.9) in summer. The low pH is probably related to metabolic depression. In our study, C. glacialis reduced its metabolic enzyme activity to half when residing at the overwintering depth. Strong seasonal patterns were also seen in respiration and digestive enzyme activities which correlated well with C. glacialis ontogenetic migration. True diapause is defined as arrested development and reproduction, and reduced metabolic activity in a torpid state. The diapause intensity of C. glacialis seems to be less and with a greater potential for flexible physiological adjustments compared to the profound metabolic adjustments found in copepods from the deep open ocean. A newly developed lifestrategy model succeed to explain why Calanus glacialis dominate in colder more Arctic environments, and the smaller North Atlantic sibling species Calanus finmarchicus in more temperate environments. Important regulating factors showed to be the length of the productive season, temperature and the mortality risk. Overall our results show that C. glacialis has a flexible life strategy, but it is uncertain whether it is able to maintain the same large population under more temperate conditions. An element of uncertainty that needs to be studied is increased competition and predation pressure when a milder climate allows temperate species to establish themselves in the Arctic. This highly international 3-year project has so far resulted in one completed PhD thesis and 3 completed master theses. At present seven papers are published, two articles are in review, and 11 manuscripts are in progress. For more information see (http://www.mare-incognitum.no/index.php/cleopatra-ii).

A warmer climate with less extensive ice cover will lead to higher total primary production in the Arctic, which has the potential to increase the overall secondary production. However, altered climate conditions will affect timing, quantity and quality o f ice algal and phytoplankton food sources with extensive implications for grazers. Depending on the grazers ability to adapt to these new conditions, some organisms will be favored more than others, resulting in ecological winners and losers. We therefor e propose a project that will study Arctic zooplankton and their capability to adapt their current life history strategies and physiology to a changing Arctic. We will focus in our study on Calanus glacialis, the key herbivore in Arctic shelf seas, and c ombine field and laboratory investigations with model development to ultimately arrive at an improved understanding of the physiological and life history adaptations of Arctic zooplankton. A central element of our approach is to move towards individual-b ased zooplankton ecology where states, such as lipid reserves, are measured at the level of individuals. We aim at a tight linkage between data collection through field and experimental studies and the modelling work where models deliver predictions for f ield and laboratory work, securing target-aimed field investigations and well-defined hypotheses. In turn, findings from field and experimental work do not only test model predictions, but also deliver a better basis for improved parameterization and desi gn of models. Long-term data-series acquired through previous projects will be continued and will allow us to include inter-annual variability and different ice-cover scenarios in our investigations. This project will include several national institutions and international collaborators, with strong participation by early career scientists.